The invention relates to an air-supplied dry cooler for condensing steam.
It is known to use air for condensing turbine steam. With direct air-cooled condensation, the turbine steam is condensed in ribbed pipe elements (surface condensers) connected in parallel, and the condensate is returned to the feed water loop. The interior of the ribbed pipe elements is under vacuum, with the non-condensable gases being suctioned off. The cooling air flow is generally produced with fans, rarely by natural airflow. Dry coolers with a roof structure (A-arrangement) are widely used. The ribbed pipe elements form hereby the legs of a triangle, with the fans arranged at the base.
The surface condensers can be connected in two ways: on one hand, in a direct-flow condenser arrangement and, on the other hand, in a counter-flow arrangement (dephlegmator arrangement). In the direct-flow condenser, the steam flows from a distribution line located at the top downwards into the direct-flow condenser. The condensate which also flows downwards is collected in a condensate collection line. In the counter-flow condenser arrangement, the exhaust steam is introduced into the cooling pipes from below and flows therefore against the discharged condensate. In practical applications, direct-flow condensers and the counter-flow condensers are combined with one another. The so-called “condensation end” of the steam is then located in the counter-flow condenser.
It is known to provide an intermediate bottom with recesses (DE-GM 18 73 644) in the steam distribution chamber in order to uniformly distribute the steam flow introduced into the steam distribution chamber of a counter-flow condenser. The total flow cross-section of the recesses is sized smaller than the total cross-section of the condenser pipes.
Conversely, it is known from DE 44 39 801 C2 that most of the dephlegmators have resistance elements in the region of their ends facing the gas collector. The exhaust steam then experiences a resistance caused by the introduced uniform distribution of the steam entering the individual dephlegmator pipes from below. With this introduced uniformity, the entire condenser surface is predominantly utilized for the condensation, preventing the formation of “cold nests” or “dead zones”, where neither exhaust steam nor condensate is present. However, problems may arise in certain situations when larger quantities of the condensate accumulate in the suction chamber at low temperatures. The large quantities of condensate can cause supercooling and in extreme situations even freezing of the condensate. This danger exists at outside temperatures below freezing, both during operation and during startup, because the large quantity of frozen condensate located just below the baffle opening may not be thawed quickly enough by the gas-steam mixture, so that the newly generated condensate quickly freezes and may in extreme situations block the baffle openings.
Another problem can arise when large quantities of condensate accumulate in the suction chamber, which must be returned to the dephlegmator pipes through the same opening through which the gas-steam mixture enters the suction chamber. The counter-flow through the gas-steam mixture can produce “swallowing” in the region of the individual openings, temporality separating the gas-steam flow. This may cause undesirable pressure variations inside the individual dephlegmator pipes.
It is an object of the invention to improve an air-supplied dry cooler for condensing steam so as to attain a high overall efficiency, and to reliably prevent freezing of the dephlegmator, and separation of the gas-steam flow entering the suction chamber.